Ancient Athens was a remarkably peaceful and well-ordered society by both ancient and contemporary standards. Scholars typically attribute Athens’ success to internalized norms and purely informal enforcement mechanisms. This article argues that the formal Athenian court system played a vital role in maintaining order by enforcing informal norms. This peculiar approach to norm enforcement compensated for apparent weaknesses in the state system of coercion. It mitigated the effects of under-enforcement in a private prosecution system by encouraging litigants to uncover and punish their opponents’ past violations. Court enforcement of extra-statutory norms also permitted the Athenians to enforce a variety of social norms while maintaining the fictions of voluntary devotion to military and public service and of limited state interference in private conduct.